1. Field of the Invention
The present invention relates to fluorinated polyimides with high heat resistance as well as low dielectric constant, a low thermal expansion coefficient and low birefringence and low water absorption, which can be used for electric and electronic devices, optical materials, machine parts and the like, to laminated substrates employing the fluorinated polyimides, and to polyamic acid solutions comprising polyamic acids, which give fluorinated polyimides, dissolved in organic solvents.
2. Description of the Related Art
Polyimides, which have excellent heat resistance coupled with superior electrical and mechanical properties, have conventionally been applied for a variety of uses as industrial materials, especially in the field of electronic devices.
These commonly used polyimides, however, while having excellent heat resistance, electrical properties and mechanical properties, do not always exhibit satisfactory properties for all uses.
For example, in terms of electrical properties, polyimides used for interlayer insulating films in the field of semiconductors do not sufficiently satisfy demands from the standpoint of their dielectric constant, and, therefore, a further reduction in the dielectric constant of polyimides is desired.
In order to reduce the dielectric constant, in light of this desire, diamines are used which contain fluorine atoms in the molecular backbones of the diamines as structural monomers of the polyimides, or monomers are used which include fluorine-containing groups in the molecular backbones of the tetracarboxylic dianhydrides which are the other structural monomers, to thereby achieve lower dielectric constant in the resulting polyimides. Similar methods are adopted to lower birefringence as well.
For example, in Japanese Unexamined Patent Publications No. 4-47933, No.4-235034, No.4-239037 and elsewhere there is disclosed the use of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl as the diamine component for polyimides with various aromatic tetracarboxylic anhydrides, which provides an effect of lower dielectric constant. Also, in Japanese Unexamined Patent Publication No. 4-77587 it is disclosed that a lower dielectric constant and a lower thermal expansion coefficient can be achieved with polyimides which are combinations of acid anhydrides that are specifically aromatic tetracarboxylic dianhydrides wherein the aromatic ring is substituted with a fluorine atom-containing organic group, and aromatic diamines wherein the aromatic ring is substituted with a specific organic substituent.
In addition, Japanese Unexamined Patent Publication No. 5-178991 teaches that an effect of lower dielectric constant is achieved for polyimides obtained using 3,3'-diamino-5,5'-bis(trifluoromethyl) diphenyl ether as the aromatic diamine component with various acid anhydrides. Japanese Unexamined Patent Publication No. 7-292105 discloses that polyimides made from 2,6-bis(3-aminophenoxy)-3-trifluoromethylpyridine and various acid anhydrides can provide lower dielectric constant.
Although these disclosed compounds exhibit high performance in terms of individual properties, problems still remain such as an inability to form polyimide films because of insufficient molecular weight of the polyamic acids, or difficulties in the industrial production of the starting monomers.